A number of pentacoordinated phosphorus compounds have been prepared by condensations of trivalent compounds with a cyclic four-membered ring dithietene, by addition to various dienes, and by reactions of dioxetanes. These materials have been characterized where possible by Hl, P31 and, in some cases, F19 and C13 NMR spectroscopy. Their permutational isomerizations have been investigated by variable temperature NMR measurements. In a series of polycyclic compounds the rates of isomerization were found to be significantly affected by the presence of a five-membered ring in the caged system. During the past year, one hundred and three compounds were submitted for testing. So far two of these materials, both of which are phosphonium salts, have shown activity, and currently larger quantities are being prepared. The reactions of aryl alkyl sulfinates, ArSOR, with phosphites yields phosphoranes, (RO)P5. A large number of these have now been prepared. BIBLIOGRAPHIC REFERENCES: B.S. Campbell, D.B. Denney, D.Z. Denney and L. Shih, "Reactions of Dioxetanes with Sulfoxylates and Sulfides. Preparation of Novel Tetraalkoxysulfuranes," J. Amer. Chem. Soc., 97, 3850 (1975). L.L. Chang and D.B. Denney, "Reactions of Tri-t-Butylphosphite with t-Butyl and n-Butyl Hypochlorites," Phosphorus, 6, 69 (1975).